The reliability of electrical power system devices such as electrical motors, generators and transformers is of critical importance in many industries and service providers. For example, failure of electrical motors in many process industries may result in costly plant shutdowns. Likewise, failure of motors in water supply system applications can lead to widespread loss of potable or fire protection water. Loss of generators or distribution transformers may lead to widespread power outages and unsafe conditions. Many operators of electrical power system devices are looking to predictive maintenance technologies to reduce costs and improve safety of operations.
Many technologies are available to detect possible problems with mechanical components in motors and generators, such as bearings. With enough warning, these components may be replaced or repaired during scheduled outages instead of during costly unplanned shutdowns.
However, many failures in electrical power system devices result from failure of the insulation system itself. For example, insulation varnish in a motor may degrade and become brittle with age. Under stress, the insulation itself may crack and fail, resulting in coil shorting and shutdown of the motor.
Currently, there are limited means to detect degradation of insulation systems in electrical power system devices. One of the most common methods to approach the problem is to assign an operational life based on manufacturer's recommendations or operator's experience. Upon completion of the expected life, the device is replaced or re-wound. This method is often inadequate since the local environmental conditions can have a substantial effect on the life of the insulation. For example, a 10 degree Celsius increase in temperature of the insulation system may decrease the lifetime of the insulation system by one-half. Load changes, or blocking of cooling air can have a substantial effect on device lifetime that scheduled replacement methods cannot predict.
Visual and tactile inspections are another method used in some commercial and industrial applications. Visual inspections are often difficult because much of the insulation system may not be visible and device disassembly is required. These inspections are time consuming, very subjective in nature and have poor capability for predicting remaining life.
Another common method to monitor insulation condition is to “megger” a motor by applying a high potential on a winding and measure leakage current. While this method is effective in finding existing problems resulting from insulation failure, it is of very limited effectiveness in forecasting future insulation failure. Installed systems are very costly and portable systems require shutting down the equipment and lifting leads in order to test.
Other methods for measuring insulation system condition and predicting remaining life include partial discharge and phase analysis technologies. The equipment required for these methods is very costly, in some cases is only effective on high voltage equipment. These methods are of limited effectiveness in predicting remaining life and require specialized training.
An improved method is needed to monitor the condition of electrical power system devices and to predict remaining life.